(1) Field of the Invention
The present invention relates to an asphalt composition containing a hydrogenated conjugated diene copolymer with a specific structure. More particularly, the present invention relates to an asphalt composition comprising 0.5 to 50 parts by weight of a hydrogenated conjugated diene copolymer (a) and 100 parts by weight of asphalt (b), wherein the above described hydrogenated conjugated diene copolymer (a) comprises a polymer block (A) comprising vinyl aromatic monomer units and at least one hydrogenated copolymer block (B) obtained by hydrogenation of a non-hydrogenated random copolymer block comprising conjugated diene monomer units and vinyl aromatic monomer units, the above described hydrogenated conjugated diene copolymer (a) having the following characteristics (1) to (5):
(1) the content of the above described vinyl aromatic monomer units is more than 30% and not more than 60% by weight per weight of the above described hydrogenated conjugated diene copolymer;
(2) the content of the above described polymer block (A) is from 5% to 50% by weight per weight of the above described hydrogenated copolymer;
(3) the weight average molecular weight is from 30,000 to 500,000;
(4) the percentage of hydrogenation of the double bonds in the above described conjugated diene monomer units is from 60% to 100%; and
(5) at least one peak of the loss tangent (tan δ) is present in the range of from −40° C. to less than −10° C. in a dynamic viscoelastic spectrum obtained with respect to the above described hydrogenated copolymer.
The asphalt composition of the present invention has high softening point, modulus and elongation and is excellent in high-temperature storage stability. In particular, the asphalt composition has extremely high softening point and modulus even when it contains a low content of the hydrogenated copolymer. Furthermore, the asphalt composition has excellent high-temperature storage stability even when it contains a high content of the hydrogenated copolymer. The asphalt composition of the present invention can be suitably utilized for road pavement, roofings/waterproof sheets and sealants, by making the most of such characteristics. In addition, the asphalt composition is very suitable for roofing shingles since it is also excellent in weatherability in addition to the above characteristics.
(2) Description of Related Art
Asphalt compositions have been widely used for applications such as road pavement, waterproof sheets, sound isolation sheets, and roofings. Various attempts have been made to improve the properties by adding various polymers to asphalt. Specific examples of these polymers include ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, rubber latexes, block copolymers consisting of conjugated dienes, and vinyl aromatic hydrocarbons and the like.
In recent years, there is an increasing demand for asphalt mixtures with excellent strength and abrasion resistance associated with circumstances such as the increase or speedup of vehicles passing through roads. This requires a higher softening point and mechanical strength such as modulus, and the improvement of these strength properties has been attempted, for example, by increasing the molecular weight of the above block copolymers. However, the asphalt composition obtained according to such a method does not provide sufficient storage stability during high-temperature storage, resulting in separation of polymers from the asphalt composition, increase in melt viscosity and reduction of workability for road pavement.
Consequently, the improvement of storage stability has been generally attempted by adding an aromatic oil or crosslinking by adding sulfur or peroxides. For example, JP-B-57-24385 (corresponding to U.S. Pat. No. 4,145,322) discloses the use of sulfur, and JP-A-03-501035 (corresponding to U.S. Pat. No. 5,508,112) discloses the combination of sulfur, a vulcanizing agent and a vulcanization accelerator containing sulfur. However, such improvement methods have not yet provided adequate results and a further improvement has been desired.
In addition, US Patent No. 2003/0149140 discloses an asphalt composition using a copolymer consisting of a conjugated diene with a special structure and a vinyl aromatic hydrocarbon. However, the above described composition is inadequate in the balance of the softening point, modulus, and high-temperature storage stability and is poor in weatherability and low-temperature characteristics. Therefore, a further improvement has been desired.
In addition, U.S. Pat. No. 6,120,913 discloses an asphalt composition for roofing shingles comprising a block copolymer consisting of a vinyl aromatic hydrocarbon and a conjugated diene and fillers. However, since the above described composition uses a common block copolymer consisting of a vinyl aromatic hydrocarbon and a conjugated diene, it is inadequate in high-temperature storage stability and poor in weatherability, therefore, a further improvement has been desired for use in roofing shingles.